Contoured composite structural mambers and methods for making the same

ABSTRACT

Contoured composite structural members and methods for making the same are described. The contoured structural members comprise composite materials and the contoured structure can be provided by tube rolling (or roll wrapping) the composite materials together and then, if necessary, bonding them or connecting them. The outer surface of the structural member can be provided with a polygonal shape during the process of manufacturing. With a contoured structure and an outer polygonal shape, applications for the structural members of the present invention are increased.

REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. provisional patentapplication No. 60/216,636, the entire disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to structural members and methodsfor making the same. In particular, the present invention relates tocontoured composite parts and methods for making the same.

BACKGROUND OF THE INVENTION

[0003] In recent years there has been an increasing emphasis on the useof lightweight composite materials. One application, for example, hasbeen their use to improve the efficiency of motor vehicles. To that end,the United States Government and the U.S. Council for AutomotiveResearch (USCAR)—which represents Daimler Chrysler, Ford, and GeneralMotors have partnered to form the Partnership for a New Generation ofVehicles (PNGV). One goal of PNGV is to develop technology, such ascomposite technology, that can be used to create environmentallyfriendly vehicles with up to triple the fuel efficiency, while providingtoday's affordability, performance and safety. For example, PNGV wantsto improve the fuel efficiency of today's vehicles from about 28 milesper gallon (mpg) to about 83 mpg and a 40-60% decrease in the presentcurb weight (3200 pounds).

[0004] One method to improve the fuel efficiency is to decrease theweight of today's vehicles and use lighter weight materials. Thematerials used in today's vehicles, such as steel and aluminum, arequite heavy relative to composite materials, but have been necessary toprovide sufficient structural properties, including tensile,compression, flexural, interlaminar shear, and in-plane shear strengthsand other mechanical and material properties, to meet vehicle designrequirements.

[0005] Many other applications of lightweight composites have been madeto supplement or replace the use of structural materials, such as steel,cast iron, and aluminum. These include buildings, bridges, recreationalvehicles, aerospace, defense, and sporting goods, as well as many otherapplications.

[0006] Composites are a mixture or combination, on a macro scale, of twoor more materials that are solid in the finished state, are mutuallyinsoluble, and differ in chemical nature. Types of composites includelaminar, particle, fiber, flake, and filled composites. Composites,however, often have not had the combination of structural propertiesmentioned above and/or low cost necessary to promote their widespreaduse in motor vehicle and other applications.

[0007] Despite their lack of structural strength, some compositematerials have been employed in vehicle manufacturing. For example,laminated composite tubes above have been used as structural members invehicles as well as other structures. Typically, the tube is generallystraight over its length, e.g., the radius remains constant along thelength of the tube. As well, the tubes are generally circular incross-section. See, for example, U.S. Pat. Nos. 4,128,963, 4,946,721,4,968,545, 5,061,533, Re35,081, 5,348,052, 5,447,765, 5,437,450,5,499,661, 5,579,809, 5,624,115, and 5,725,920, the disclosures of whichare incorporated herein by reference. Such structural members, however,have been typically limited to the structures described above and sotheir end-use and applications have been quite limited.

SUMMARY OF THE INVENTION

[0008] The present invention provides contoured composite structuralmembers and methods for making the same. The contoured structuralmembers comprise composite materials and the contoured structure can beprovided by tube rolling (or roll wrapping) the composite materialstogether and then, if necessary, bonding them or connecting them. Theouter surface of the structural member can be provided with a polygonalshape during the process of manufacturing. With a contoured structureand an outer polygonal shape, applications for the structural members ofthe present invention are increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIGS. 1-16 are views of structural members and methods of makingthe same according to the present invention. FIGS. 1-16 presented inconjunction with this description are views of only particular—ratherthan complete—portions of the structural members and methods of makingthe same.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The following description provides specific details in order toprovide a thorough understanding of the present invention. The skilledartisan, however, would understand that the present invention can bepracticed without employing these specific details. Indeed, the presentinvention can be practiced by modifying the illustrated structuralmember and method and can be used in conjunction with apparatus andtechniques conventionally used in the industry.

[0011]FIG. 1 illustrates one contoured structural member—a tubularmember with a substantially circular cross-section—according to thepresent invention. In the context of the present invention, a“contoured” structural member is any shape, size, or configuration whereat least one portion of the outer or inner periphery of such member issubstantially non-flat, including curved, geometric or irregular.Preferably, the contoured structural members have a closed surfaceconfiguration, such as a surface that facilitates their manufacture asexplained below. In the context of the present invention, a “closed”structural member is one having any shape, size, or configuration whereat least one portion of the surface (inner and/or outer) of such memberis a substantially closed or substantially continuous. Examples of aclosed configuration include a tubular, substantially spherical,polygonal, conical, or other similar shape, as well as those illustratedand described herein.

[0012] The structural members of the present invention may have acylindrical or a non-cylindrical configuration such as cones, pyramid,pods, hemispheres or spheres. The structural members of the presentinvention may also have a circular or a non-circular cross-section suchas rectangular, square, hexagonal, octagonal, or the like. They may alsocomprise very irregular, non-closed, substantially planar surfaces.Indeed, the structural members of the present invention could have anycomplex contoured shape or combination of contoured shapes.

[0013] In FIG. 1, tubular structural member 2 comprises inner section orportion 4, optional intermediate portion or section 6, outer section orportion 8, and optional core region 10. Inner portion 4, outer portion8, and optional core region 10, can be made of any suitable compositematerial as described below. Core region 10 is located in an innersection of structural member 2 and, as described below, is about thesize of the substrate or mandrel used in forming the structural member.Core region 10 can be of any suitable size, shape, or configurationdepending primarily on the removable mandrel(s) in the manufacturingprocess used to make structural member 2, the configuration ofstructural member 2, and the desired end application of structuralmember 2.

[0014] Core region 10 may be hollow, but may optionally be partially orcompletely filled with any desired core material such as foam, plastic,conducting or insulating materials, metals and/or the like. Core region10 containing the core material may be a structural element. The corematerial may also be added after structural member 2 is formed, orformed integrally into the structure. If the core material is addedafter the formation of structural member 2, it may be attached tostructural member 2 using an adhesive or other suitable bonding meansknown in the art.

[0015] The materials for inner section 4, optional intermediate section6, and outer section 8 can be the same or different materials.Preferably, inner portion 4 optional intermediate portion 6, and outerportion 8 comprise the same material. In one aspect of the invention,the materials for the inner or outer portions comprise any suitablereinforced resin matrix material (RRMM), which is a resin matrixmaterial (RMM) with continuous or discontinuous reinforcement materialembedded in the resin matrix. In one aspect of the invention, the RMM isa organic resin matrix material (ORMM). See, for example, U.S. Pat. Nos.5,725,920 and 5,309,620, the disclosures of which are incorporatedherein by reference.

[0016] In one aspect of the invention, the ORMM can be a thermosetresin. Thermoset resins are polymeric materials which set irreversiblywhen heated. Examples of thermoset resins include epoxy, bismeleimide,polyester, phenolic, polyimide, melamine, xylene, urethane, phenolic,furan, silicone, vinyl ester, and alkyd resins, or combinations thereof.The thermoset resins can contain various additives as known in the art,such as cross-linking agents, curing agents, fillers, binders, orultraviolet inhibitors. Preferably, epoxy, vinyl ester, or polyesterresins are employed as the thermoset resin in the present invention.

[0017] In another aspect of the invention, the ORMM can be athermoplastic resin matrix material. Thermoplastic resins are polymericmaterials which do not set irreversibly when heated, e.g., they softenwhen exposed to heat and then return to their original condition whencooled. Examples of thermoplastic resins include polypropylene,polyethelene, polyamides (nylons), polyesters (PET, PBT), polyetherketone (PEK), polyether ether ketone (PEEK), polyphenylene sulfide(PPS), polyphenylene oxide (PPO) and its alloys, and polyvinyl resins,or combinations thereof. The thermoplastic resins can contain variousadditives as known in the art, such as cross-linking agents, curingagents, fillers, binders, or ultraviolet inhibitors. Preferably,polyamides (nylons), polyester, polycarbonate and polypropylene resinsare employed as the thermoplastic resin in the present invention.

[0018] The material used to reinforce the RMM of the present inventioncan be in any form which reinforces the resin matrix. Examples ofreinforcement forms include unidirectional tape, multidirectional tapes,woven fabrics, roving fabrics, matt fabrics, preforms, fibers,filaments, whiskers, and combinations thereof. The type of material usedto reinforce the RMM can be any type serving such a reinforcingfunction. Preferably, the form of the reinforcement materials for theresin matrix is a fiberous material, such as continuous or discontinuousfibers. Examples of materials that can be employed in the presentinvention include glass-s, glass-e, aramid, graphite, carbon, ultrahighmolecular weight polyethylene, boron, silicon carbide, ceramic, quartz,metals, isotropic metals (aluminum, magnesium and titanium), metalcoated organic fibers, CAMP, hybrids of these fibers, or combinations ofthese fibers. See, for example, U.S. Pat. No. 6,117,534, the disclosureof which is incorporated herein by reference.

[0019] In yet another aspect of the invention, non- or partially-curedcomposite materials are used as the material for the inner and/or outersections. Composites are a mixture or combination, on a macro scale, oftwo or more materials that are solid in the finished state, are mutuallyinsoluble, and differ in chemical nature. Any composites known in theart such as laminar, particle, fiber, flake, and filled composites canbe employed in the invention. The non- or partially-cured compositematerials are a ORMM (thermoset or thermoplastic resin) reinforced witha continuous fiber.

[0020] Preferable composite materials used for inner section 4 and outersection 8 include B-stage prepreg materials typically in the form ofsheets or laminates, which can be formed by impregnating a plurality offiber reinforcement tows with a formulated resin. Methods of makingB-stage prepreg sheets and the sheets themselves are well known. See,for example, those sheets described in U.S. Pat. No. 4,495,017, thedisclosure of which is incorporated herein by reference. When cured,prepreg materials are generally stronger and stiffer than metals whileproviding greater resistance to fatigue, chemicals, wear and corrosion.Preferable reinforcement for prepregs include aramids, glass materials,nickel carbide, silicone carbide, ceramic, carbons and ultra-highmolecular weight polyethylene, or a combination thereof. See, forexample, U.S. Pat. Nos. 4,968,545, 5,102,723, 5,499,661, 5,579,609, and5,725,920, the disclosures of which are incorporated herein byreference. Carbon, glass, metals and especially isotropic metals likealuminum, magnesium and titanium, metal-coated organic fibers, andaramid fibers, or a combination thereof, can also be employed as thefibers. See, for example, U.S. Pat. Nos. 5,601,892 and 5,624,115, thedisclosures of which are incorporated herein by reference. Preferably,carbon fibers, glass fibers, or aramid fibers and more preferably Kevlar29 or 49 fibers are employed in the present invention.

[0021] The fiber volume in the prepregs may be varied so as to maximizethe mechanical, electrical, and thermal properties. See, for example,U.S. Pat. No. 5,848,767, the disclosure of which is incorporated hereinby reference. High fiber volume parts are stiffer and, in the case ofthermally conductive fibers, the parts are more thermally conductive.Fiber volumes in the present invention can range from about 5% to about95%, and preferably range from about 50% to about 65%. The fibers of theprepregs may be oriented within the prepreg material in any desireddirection as known in the art, such as about 0 to about 90 degrees,including equal numbers of fibers balanced in opposing directions. See,for example, U.S. Pat. No. 4,946,721, the disclosure of which isincorporated herein by reference.

[0022] In yet another aspect of the invention, sheet molding compounds(SMCs) can be used as the materials for the inner or outer portion. SMCsare sheets made up of B-stage thermoset resin reinforced with adiscontinuous fiber. SMCs are fully formulated ORMM compounds havingdiscontinuous fiber reinforcement materials which are typically formedinto sheet, ply, or laminate without additional preparation. See, forexample, U.S. Pat. No. 6,103,032, the disclosure of which isincorporated herein by reference. The resins that can be used in theSMCs of the present invention include any of the thermoset resins listedabove. Preferably, polyester vinyl esters or epoxy resins are employedas the resin in SMCs of the present invention. The fibers that can beused in the SMCs of the present invention include any of those listedabove. Preferably, glass, carbon, or aramid fibers, and more preferablyKevlar 29 or 49 fibers can be used as the fibers in the SMCs. The fibervolume in the SMC may also be varied so as to maximize the mechanicaland thermal properties.

[0023] With an unsaturated resin system as its base, SMCs incorporateother materials for desirable processing and molding characteristics andoptimum physical and mechanical properties, such as mechanical strength,impact resistance, stiffness, and dimensional stability. Theseincorporated materials include polymers, fibers for reinforcement,resins, fillers, initiators to promote polymerization, viscosity agents,lubricants, mold release agents, catalysts, thickeners, pigments,polyethylene powders, flame retardants, ultraviolet absorbing agents,and other additives. Each of the additives can provide importantproperties to the SMC, either during the processing or molding steps orin the finished parts, and can be incorporated in the SMCs of thepresent invention.

[0024] In one aspect of the invention, inner section 4, optionalintermediate section 6, and outer section 8 contain at least one layerof such ORMM materials. One layer is sufficient to form the respectiveinner or outer section and provide the desired structuralcharacteristics for structural member 2. Additional layers can be addedto improve the strength, stiffness, or other physical characteristics ofstructural member 2. It is possible to use a single layer with fibershaving complementary orientations. It is preferred, however, to use aplurality of layers with complementary orientations to balance intrinsicstresses in the layers that make up the sections that result when, asdescribed below, the B-stage materials are fully cured. To becomplementary, the fibers in successive layers should be symmetric andbalanced (e.g., by having the fibers offset from the sheet axis by equaland opposite amounts from one layer to another) as shown in FIG. 2. Thefibers can also be oriented to meet the design parameters of thecomponent into which they are being incorporated, e.g., to optimize thestructural strength against the expected load. The fibers could beoriented at any suitable angle, including at angles ranging from about 0to about 90 degrees, including in ±15, ±30, ±45, ±60, and ±75 degrees,or as otherwise known in the art. See, for example, U.S. Pat. Nos. Re.35,081 and 5,061,583, the disclosures of which are incorporated hereinby reference.

[0025] The configuration of inner portion 4 optional intermediatesection 6, and outer portion 8 can vary within structural member 2. Forexample, the materials used for the composite, the fiber orientation,and the curvature, thickness, shape and other characteristics of theinner and/or outer portions (4, 8) can differ along the length and widthof structural member 2. See, for example, U.S. Pat. No. 5,718,212, thedisclosure of which is incorporated by reference.

[0026] The structural member of the present invention may, if desired,have additional layers or portions on the outside of outer portion 8. Inone example, a layer of metal, insulation, another composite material,or honeycomb core material may be placed over outer portion 8. Numerousadditional portions or layers, including similar or different compositematerials, could be added in a similar manner. In addition, at least onestructural component, such as a bracket, coupler, cap, or the like couldbe located on the end(s) of structural member 2.

[0027] The structural member of the present invention may have anysubstantially non-flat contour or configuration. FIG. 4 illustratesseveral such configurations. In one aspect of the invention, thestructural members of the present invention can be configured with anycontoured shape known in the art. The contoured shapes can have anycombination of inner or outer shapes, inner and outer thickness, andinner or outer radii.

[0028] In preferred aspect of the invention, the structural members ofthe present invention have the contoured shapes illustrated in FIG. 12.The preferred contoured shapes have a thickness and/or a radius thatvaries—either regularly or irregularly—along the length of thestructural member. For example, referring to FIG. 12, the structuralmember 2 comprises a first portion 41 with a first diameter, a secondportion 42 with a second diameter, and a third portion 43 with a thirddiameter. As another example, as illustrated in FIG. 13, the structuralmember 2 comprises a first portion 46 with a first thickness, a secondportion 47 with a second thickness, and a third portion 48 with a thirdthickness.

[0029] In another preferred aspect of the invention, the shape of thestructural member has a shape other than substantially circular.Examples of such shapes include rectangular, hexagonal, octagonal,polygonal, etc . . . Making the tube with polygonal shape—such as ahexagon—provides several flat surfaces on the inner or outer surface ofthe structural member, which becomes important when bonding the surfaceof the structural member to another member, such as a metal end piece.An interference is created between the surface of the other member(metal end piece) and the surface of the structural member, supplyingtorsional resistance when either the structural member or the end pieceis subjected to a load. The larger the interference, the more resistanceis given to the torsion, separate from the resistance provided by thebond surface. The amount of interference is proportional to thetorsional resistance, so increasing the diameter or decrease the numberof polygon flats thereby increases the resistance to torsion, as isdepicted in FIG. 14.

[0030] Creating a polygonal shape, however, creates a secondary loadingcondition on the structural member. This loading condition is usuallylocalized near the bond surface and can easily be great enough toexplode the structural member from the inside. To protect against such aproblem, that area of the structural member 2 is “overwrapped” with acomposite collar comprising of fibers which are oriented around thecircumference of the structural member. This prevents the structuralmember from exploding, while not adding much weight. The overwrap islocated over the entire joint area with some extension past the joint tohelp with stress concentrations.

[0031] The optimum number of sides of the polygonal shape depends on theindividual design. The more sides used, the less interference there willbe and the less torsional resistance. Yet increasing the number ofpolygonal sides moves closer to a round shape. So reducing the optimumjoint strength to weight ratio will also increase the optimum tubestrength to weight ratio. The number of composite plies used in theoverwrap also depends on the design and the internal pressure due to thetorsion and the resistance to internal pressure. Obviously a thickertube would normally resist more internal pressure and require lessnumber of overwrap plies. But then it may have a significantly largerinternal pressure due to a large torsional load. As with every design,the optimum design will be the one which is the lightest for it's givenstrength and stiffness.

[0032] The structural members of the present invention can be made byany suitable process that provides the desired structure. Suitableprocess for making the composite layer(s) include any processes known inthe art, such as thermoforming, bladder or resin transfer molding, orinflatable mandrel processes, as described in U.S. Pat. Nos. 5,225,016,5,192,384, 5,569,508, 4,365,952, 5,225,016, 5,624,519, 5,567,499, and5,851,336, the disclosures of which are incorporated herein byreference. Another suitable process is a vacuum bagging process, such asdescribed in U.S. Pat. No. 5,848,767, the disclosure of which isincorporated herein by reference. Other suitable processes are afilament winding process or sheet or tube rolling (also known as rollwrapping). See, for example, U.S. Pat. Nos. 5,632,940, 5,437,450,4,365,952, 5,624,529, 5,755,558, 4,885,865, 5,332,606, 5,540,877,5,840,347, and 5,914,163, the disclosures of which are incorporatedherein by reference.

[0033] In the filament winding process, filaments of the desiredmaterial are dispersed in a matrix of binder material and wound aboutany suitable substrate, such as a mandrel assembly. Any suitable mandrelor mandrel assembly, including those described in U.S. Pat. Nos.5,795,524, 5,645,668, 5,192,384, 5,780,075, 5,632,940, 5,817,203, and5,914,163, the disclosures of which are incorporated by reference, canbe employed in the present invention.

[0034] In one aspect of the invention, the substrate or mandrel musthave sufficient strength, desired shape, and be able to withstand theprocessing conditions for making the structural member. Suitablemandrels include those made of metals like steel and aluminum,polycarbonate, thermoplastic, or RRMM materials. The mandrels may besolid or hollow. The mandrel or substrate should have a shape generallycorresponding to the desired shape (core region 10) of structural member2, e.g., the outer surface of the mandrel should have a shapecorresponding to the inner surface of the inner portion 4.

[0035] The filaments are wound over the mandrel and are reciprocallydisplaced relative to the mandrel along the longitudinal or winding axisof the mandrel to build portion 4. Additional portions, structures, orlayers, such as additional metal or composite layers, can be added asdescribed above or as known in the art.

[0036] Preferably, the present invention employs a tube rolling (alsoknown as roll wrapping) process for making the structural member of thepresent invention. One exemplary tube rolling process is illustrated inFIG. 5. The tube rolling process employs discrete sheet(s) (or plies orlaminates) of the desired composite material rather than filaments. Thesheet(s) is interleaved, wrapped, or rolled over a mandrel assembly suchas at least one mandrel 20. If desired, a release film can be applied tothe mandrel prior to rolling any materials thereon. When more than onesheet is employed, the sheets can be stacked as illustrated in FIG.2—prior to or during the rolling process—by hand or by any suitablemechanical apparatus, with the fibers of the composite material orientedin the desired orientation. After forming inner portion 4, the rollwrapping process continues to apply the material of outer portion 8.Further details about roll wrapping processes are described inEngineered Materials Handbook, Volume 1: Composites, ASM International,pp. 569-574 (1987), the disclosure of which is incorporated herein byreference.

[0037] Additional layers or materials can be added over outer portion 8,if desired, in a similar manner using any of the above processes. Byadding additional composite plies or additional composite materials atthis stage, the structural members illustrated in FIGS. 12 and 13 can becreated. For example, the “base” structural member illustrated in FIG.13, can be made by the above process. Then, additional plies (or sheets)of the desired material can be added by wrapping in the desired areas toobtain the varying the additional thicknesses. In a similar manner,additional plies can be wrapped to create the overwrap described above.

[0038] The layers of the individual portions (inner, intermediate, andouter) can be cut and/or patterned such that when roll wrapped, the endsof individual sheet(s) substantially abut when rolled, thereby forming abutt joint 30. Preferably, the butt joint formed by the ends of anysingle sheet is staggered from the butt joint formed by the ends of anadjacent sheet, as illustrated in FIG. 6.

[0039] Inner portion 4 and outer portion 8 may be formed using differentmethods. For example, inner portion 4 can be formed by filament windingand outer portion 8 by roll wrapping, or vice versa. In this aspect ofthe invention, inner portion 4 may be fully cured prior to theapplication of intermediate portion 6. Similarly, inner portion 4 andintermediate portion 6 may be applied and cured together prior to theapplication of outer portion 8. Other methods known in the art, such asthose described above, could also be combined with roll wrapping to makethe structural members by performing discrete steps by differentmethods. For example, inner portion 4 could be formed using the filamentwinding process, intermediate portion 6 and outer portion 8 could beformed using the roll wrapping process, and then this intermediatestructure could be constrained using a vacuum bagging process.

[0040] If desired, a bonding agent can be placed between successivelayers of portions 4 and/or 8. The bonding agent can be placed onselected areas only, or in a pattern such as in rows and/or columns, orover entire areas of the layer(s)/portion(s). Any suitable agent whichhelps bond the layers and is compatible with all of the processesemployed to make structural member 2 can be employed, including glues,curing agents, adhesive materials, or a combination thereof. See, forexample, U.S. Pat. No. 5,635,306, the disclosure of which isincorporated herein by reference. The bonding agent can be applied byhand or mechanical apparatus prior to, during, or after the assembly ofthe respective portion on the substrate.

[0041] Where portions 4 and 8 are successively layed up in an uncured(e.g. B-stage state), the structure has outer portion 8 overlying innerportion 4, which overlies the mandrel. If necessary to better bond andconnect inner portion 4 and outer portion 8 together, the intermediatestructure formed by these portions can be constrained. The intermediatestructure can be constrained by applying a suitable compressive force.This can be done using any suitable means including compressive dies ormolds, vacuum bagging, or by using a suitable constraining means, e.g.,by placing it in a plastic or metal mold, or by applying a suitableshrink-wrap tape(s) 22 or tube made of nylon, silicone, orpolypropylene. During the curing process described below, thecompressive means (e.g., the shrink-wrap tape or tube) applies suitablecompressive force by physical or chemical change so that the materialsof structural member 2 contact each other. When the RMM is used in theinner and/or outer portion of the present invention, the compressiveforce squeezes out excess resin during this curing process. See, forexample, U.S. Pat. Nos. 5,600,912 and 5,698,055, the disclosures ofwhich are incorporated herein by reference.

[0042] Moreover, if it is still necessary to better bond and connect thematerials in the intermediate structure, they can undergo a suitablechemical reaction. For example, when inner portion 4 and/or outerportion 8 comprise a curable material (e.g., B-stage epoxy prepreg), theintermediate structure can be cured by any suitable means 24, such as anoven curing by applying heat and/or pressure or using an ultraviolet(u.v.) or microwave curing. The necessary heat and/or pressure depend onthe size of the mandrel assembly and the materials used in structuralmember 2. During the curing process, the shrink-wrap tape or tubeapplies suitable compressive force. When the RMM is used in the innerand/or outer portion of the present invention, the compressive forcesqueezes out excess resin during this curing process.

[0043] The above process can be modified for structural members nothaving a substantially circular cross-section, including those withouter diameters having at least one flat area or area where the degreeof curvature is substantially different from other surfaces ofstructural member 2. Examples of such structural members are illustratedin FIG. 4. As illustrated in FIG. 7, where the outer diameter has atleast one relatively flat area, the shrink-wrap material (andaccompanying compressive force) applied to the intermediate structuremay not be uniform. Thus, bonding and connecting the materials to oneanother may not be uniform and, therefore, might impair the integrity ofstructural member 2. To more uniformly bond and connect such materials,at least one pressure distributor 26 is placed over the relatively flatareas of outer portion 8 prior to applying the shrink-wrap material. Thepressure distributors “distribute” the applied compressive force moreevenly to such flat areas, allowing a more uniform compressive force toall areas of the intermediate structure.

[0044] Any suitable shape of pressure distributors which evenlydistribute the applied compressive force to the intermediate structurecan be employed in the present invention. Exemplary shapes of thepressure distributors include substantially semicircular shapes (whichprovide a substantially circular outer surface) and T-shapeddistributors where the flat end of the “T” abuts (and matches in size)the flat area of the intermediate structure and the long-end of the “T”extends outwards. Other shapes and configurations, including singlecomponents rather than plural components, could be employed providedthey evenly distribute the compressive force over the flat area(s). Forthe structural member 2 like the one illustrated in FIG. 4,substantially semicircular pressure distributors 26 are depicted in FIG.7. The pressure distributors of the present invention can be made of anysuitable material that will maintain its shape when subjected to thecompressive force, such as aluminum, steel, and silicone. Preferably,aluminum is employed as the material for the pressure distributor.

[0045] The shrink-wrap material can be placed under and/or over thepressure distributor(s). The shrink-wrap materials underlying thepressure distributors pressurize the comers, as well as keeping thepressure distributors from sticking to the intermediate structure. Theshrink-wrap materials overlying the pressure distributors pressurize theflat areas.

[0046] The above process can be also be modified for structural memberswhere the inner and outer portion do not have the same shape, such asthose depicted in FIG. 11. Any suitable process modification whichmanufactures differently-shaped inner and outer portions can be employedin the present invention. The following two modifications to the aboveprocess demonstrate this concept. Other modifications could beenvisioned, even though not demonstrated below.

[0047] First, the inner portion can have a substantially circularcross-section and the outer portion a non-circular cross-section. Insuch an instance, and as shown in FIG. 8, the process for making acircular-shaped structural member is followed as described above. Tochange the shape of the outer portion, a number of pressure distributorsare placed over the circular-shaped outer portion prior to theconstraining and curing stages. The number of pressure distributors usedcorresponds to the number of flat sides desired, e.g., four for asquare, six for a hexagon, etc . . . The process as noted above is thencontinued for the constraining and curing stages. During theconstraining and curing process, the circular outer shape is changed toflat sides of the desired polygonal shape by the pressure exerted viathe pressure distributors.

[0048] Second, the inner portion can have a substantially polygonalshape (i.e., hexagon) and the outer portion a substantially circularshape. In this aspect of the invention as depicted in FIG. 9, theprocess for making a hexagonal-shaped structural member is followed asdescribed above. To change the shape of the outer portion, the pressuredistributors that are normally placed over the outer portion prior tothe constraining and curing stages are omitted. Thus, the square-shapedouter portion is just wrapped with the constraining means. The processas noted above is then continued for the constraining and curing stages.During the constraining and curing process, the outer shape is changedto a substantially circular shape by the pressure exerted via theconstraining means.

[0049] When used, the constraining means are then removed from theintermediate structure. For the plastic or metal mold, the mold isopened and removed. The shrink-wrap tape or tube may have reacted duringthe curing process to form a thin shell and, if desired, may be removedby hand or by a mechanical apparatus. When used, the pressuredistributors are also removed.

[0050] In another aspect of the invention, the constraining means can beleft on the outer portion either temporarily or permanently. Forexample, the shrink-wrap tape could be left on the structural member inthe form as a thin shell for protection during shipping and then removedlater. In another example, the shrink-wrap tape could be left on thestructural member permanently as a protective coating.

[0051] Through the constraining and curing processes described above,the inner portion and the outer portion are chemically attached and/oror connected to the intermediate portion. Preferably, the materials ofthe inner and outer portion both chemically bond to the material of theintermediate portion, thus forming a substantially permanent physicalbond.

[0052] Next, the substrate or mandrel may be removed from structuralmember 2 to form core region 10. The mandrel may be removed by anysuitable process, including any known in the art which safely removesthe mandrel without adversely impacting structural member 2, such asthose disclosed in U.S. Pat. Nos. 5,900,194 and 5,306,371, thedisclosures of which are incorporated herein by reference. If desired,core region 10 can be filled by any desired material as known in theart.

[0053] The mandrel can be either a removable mandrel or an integralmandrel. A removable mandrel is a mandrel that, as described above, isused in the roll wrapping process and then removed to create interior10. An integral mandrel is a mandrel which becomes part of structuralmember 2 and is not removed. Thus, the mandrel remains in core region 10and becomes a part of structural member 2.

[0054] When using an integral mandrel, the structural member 2 and theprocess for making that member are modified from the above description.In this aspect of the present invention, the intermediate portion isprovided over the integral mandrel, and then the outer portion isprovided over the intermediate portion. The structural member thenfollows the processing described above, with the exception that theintegral mandrel is not removed. Thus, the integral mandrel can serve asthe inner portion. If desired, an inner portion could still be includedover the integral mandrel, yielding a structural member with an integralmandrel, an inner portion, an intermediate portion, and an outerportion.

[0055] Once formed, the structural members of the present invention canbe modified or cut for any desired use. For example, the structuralmembers illustrated in FIGS. 5 and 7-9 have been cut in half along itslength to provide two structural members. Likewise, the structuralmembers could be cut along its length to provide any number of memberswith the desired length(s). Numerous shapes and configurations can bemade using by cutting along any dimension of the structural members,especially when combined with the broadest aspects of the processes ofthe present invention. A few examples of the shapes and configurationsobtained by cutting the structural members in the above manner are shownin FIG. 10.

[0056] In a preferred aspect of the invention, and as illustrated inFIG. 15, selected portions of the outer portion 8 are provided with anoverwrap 6. The overwrap can be provided by any means known in the art.Preferably, the overwrap is provided by selecting the desired size (andthickness) of the plies 50 needed to form the overwrap and then rollwrapping these plies 50 over the selected portions of the outer portion8. The structural member can then be cut radially in the middle of theoverwrap, thereby providing two or more structural members withoverwrapped portions on one—or both—of their ends.

[0057] After cutting the structural members of the present invention,additional structural components can be added. Any structural componentknown in the art can be added to the modified structural member, such asa bracket, fastener, coupler, cap, or the like. In a preferred aspect ofthe invention, the structural members have a metal end piece bonded inan the end thereof, thereby creating a structural part for torque typeapplication which can be used as a drive shaft, half shaft, or likewise.

[0058] Further modifications—other than just cutting—can be made to thestructural members of the present invention. For example, channels,holes, patterns, and similar modifications can be made in the inner orouter surface of the structural member for many reasons, such as toattach a structural component, modify the surface properties, or asimilar purpose.

[0059] Roll wrapping is the preferred method for making the structuralmembers of the present invention. The other methods described above,however, could be combined with roll wrapping to make the structuralmembers by, in one aspect of the invention, performing discrete steps bydifferent methods. For example, inner portion 4 could be formed usingthe filament winding process, the intermediate portion 6 and the outerportion 8 could be formed using the roll wrapping process, and then theintermediate structure could be constrained using the vacuum baggingprocess.

[0060] The structural member of the present invention has numerous usessuch as a tie, torsion-bar, tube, beam, column, cylinder and the likeand can be used in numerous industries. Primarily, the structural membercan be used whenever a lightweight, strong, cylindrical object isrequired. The structural member of the present invention can be used inthe automotive, transportation, aerospace, and defense industries inapplications such as airplane components, vehicle components such astracks, trains, shipping containers, defense-related applications,recreational applications such as bikes, sail masts, shafts for golfclubs and racquets, or commercial applications such as bridges andbuildings.

[0061] The following non-limiting examples illustrate the presentinvention.

EXAMPLE 1

[0062] A hollow, cylindrical structural member with a circularcross-section outside and hexagonal inside was made according tofollowing process. A thin coat of a release material (Frekote 700NC orAxel EM606SL/SP) was applied to a 0.3125″ radius hexagonal aluminummandrel with six equilateral outer sides of 0.3125 inch and a length of56 inches.

[0063] Nine pairs of B-stage prepreg laminate sheets (18 individualsheets) containing anisotropic carbon fibers were cut to a length ofabout 2.25 to about 2.84 inches in width and about 52 inches in length.The sheets each have different widths according to their location in thelay-up on the mandrel, e.g., each layer sufficiently wide to formclosely-spaced butt joints when the layer is wrapped around the mandrel.The individual laminate sheets were then overlaid so the fibers insuccessive sheets were symmetric and balanced at angles of ±45 degrees.The air between the stacked sheets was removed by using a roller orother suitable device. The stacked prepreg sheets were then roll wrappedby hand around the aluminum mandrel with a butt joint.

[0064] A first set of two strips of unidirectional tape containinganisotropic carbon fibers were cut to a length of about 10 inches andabout 1 inch in width. A second set of two more strips of unidirectionaltape containing anisotropic carbon fibers were cut to a length of about10 inches and about 2 inches in width. The first set of strips werewrapped on the prepreg sheets to create an outer set of overwraps,leaving about 0.5 inch from each end without any overwrap (e.g., themiddle of the overwrap is located 1 inch from the end). Similarly, thesecond set of strips were wrapped on the prepreg sheets to create aninner set of overwraps located so the middle of the overwrap is about17.5″ from the ends. Given the length of the overwraps and the outercircumference of the prepreg layers on the mandrel, both the inner andouter sets of overwrap contained five layers.

[0065] Next, the resulting intermediate structure was shrink-wrapped.One layer of polyethylene-based shrink-wrap tape was roll wrapped by ashrink-wrapping machine using gauge number 150 on the resultingstructure. Another layer of nylon-based shrink-wrap tape was then rollwrapped by a shrink-wrapping machine using gauge number 200.

[0066] After this wrapping process, the final structure was subjected toa curing process at about 250 degrees Fahrenheit for about 120 minutesduring which the shrink-wrap tapes applied compressive pressure to theintermediate structure. After this curing process, the shell (formed bythe shrink-wrap tapes during the curing process) was removed by handwith a knife. The mandrel was then removed from the center of the tubeby hand.

[0067] The half-inch section from each end (with no overwrap) of theresulting structural member was cut off and discarded. The rest of thetube was cut into three, substantially equal 17-inch sections with abouta 1″ wide overwrap on each end using 0.125 inch thick diamond saw. Thus,three 17″ torque tubes were created with the following characteristics:a hexagonal inside and circular outside cross-section, 18 compositelayers (or sheets), and 1 inch overwraps at each end containing 5composite layers (or sheets).

[0068] Similar torque tubes were then created. A first group of torquetubes were created similar to the above process, but having 10, 12, 14,and 16 composite sheets instead of 18 composite sheets. A second groupof torque tubes were created similar to the above process, but having 3,10, and 15 composite layers in the overwraps instead of the 5 compositeslayers.

[0069] The torque tubes were subjected to the following torque test.First, a solid equilateral hexagonal low carbon steel shaft with about0.312″ sides was cut into one-inch long sections. Half of section wascleaned with acetone to remove any oil and other contaminants, sandblasted, and then cleaned again with acetone. The clean section of asteel shaft was then bonded to a torque tube using Hysol EA 9430adhesive, leaving about 0.5 inch section of the steel shaft exposed. Thetorque tubes (with inserted steel shaft) were then oven cured for onehour at 200° F. The torque tubes with the inserted steel shaft weretested at room temperature using CDI Torque Wrench (Model Number 6004CFII). The torque wrench records only maximum torque between 60 and 600Ft-Lbs, with an accuracy of +/−1%.

[0070] The test results are reported in FIG. 16. The results indicatedthat the steel shaft broke at different points depending on the numberof composite layers in the tube and the number of composite layers inthe overwrap. Although not reflected in Table 1, generally the torque ofany composite shaft depended on the type of materials used, the radiusof tube, polygon shape and size, the number of layers in the compositetube, the configuration of composite layup, and the number of overwraplayers.

[0071] Having described the preferred embodiments of the presentinvention, it is understood that the invention defined by the appendedclaims is not to be limited by particular details set forth in the abovedescription, as many apparent variations thereof are possible withoutdeparting from the spirit or scope thereof.

I claim:
 1. A contoured structural member, comprising: at least onecontoured inner layer comprising a composite material; at least onecontoured outer layer comprising a composite material; and wherein anouter surface of the structural member has a polygonal shape.
 2. Thestructural member of claim 1, wherein the structural member has a closedconfiguration.
 3. The structural member of claim 2, further comprisingan interior region defined by an inner surface of the at least one innerlayer.
 4. The structural member of claim 3, wherein the interior regionis hollow, partially filled, or completely filled.
 5. The structuralmember of claim 3, wherein the at least one of the composite materialsis formed from a prepreg material.
 6. The structural member of claim 5,wherein the prepreg material comprises a plurality of layers.
 7. Thestructural member of claim 6, wherein the plurality of layers have aplurality of fibers with an orientation ranging from 0 to about 90degrees.
 8. The structural member of claim 1, wherein the structuralmember has at least one end with the at least one initiator not locatednear the at least one end.
 9. The structural member of claim 1, furthercomprising a composite overwrap on a portion of the outer surface of thestructural member.
 10. A contoured structural member, comprising: atleast one contoured inner layer comprising a composite material; atleast one contoured outer layer comprising a composite material; and acomposite overwrap on a portion of the at least one contoured outerlayer; wherein an outer surface of the structural member has a polygonalshape.
 11. A contoured structural member, comprising: at least onecontoured inner layer comprising a reinforced resin matrix material; atleast one contoured outer layer comprising a reinforced resin matrixmaterial; and wherein an outer surface of the structural member has apolygonal shape.
 12. The structural member of claim 11, furthercomprising a composite overwrap on a portion of the outer surface of thestructural member.
 13. A contoured structural member, comprising: atleast one contoured inner layer comprising a reinforced resin matrixmaterial; at least one contoured outer layer comprising a reinforcedresin matrix material; and a composite overwrap on a portion of the atleast one contoured outer layer; wherein an outer surface of thestructural member has a polygonal shape.
 14. The structural member ofclaim 13, further comprising a composite overwrap on a portion of theouter surface of the structural member.
 15. A method for making acontoured structural member, comprising: providing at least one innerlayer comprising a composite material; providing at least one outerlayer over the at least one inner layer, the at least one outer layercomprising a composite material; connecting the at least one inner andouter layer to the at least one inner layer; and providing an outersurface of the structural member with a polygonal shape.
 16. The methodof claim 15, including providing the at least one inner layer by rollwrapping the at least one inner layer over a substrate.
 17. The methodof claim 16, including providing the at least one outer layer by rollwrapping the at least one outer layer over the at least one inner layer.18. The method of claim 17, further including removing the substrate.19. The method of claim 18, including partially or completely fillingthe interior created by removing the substrate.
 20. The method of claim19, further including constraining the at least one outer layer andreacting any reactable material of the at least one inner or outerlayers prior to removing the substrate.
 21. The method of claim 20,including constraining the at least one outer layer by roll wrapping atleast one layer of a shrink-wrap material over the at least one outerlayer.
 22. The method of claim 21, including removing the at least onelayer of the shrink-wrap material after the reaction.
 23. The method ofclaim 20, further including providing a plurality of pressuredistributors over the at least one outer layer while constraining theouter layer.
 24. The method of claim 23, wherein the plurality ofpressure distributors provides the outer surface with the polygonalshape.
 25. The method of claim 15, further including providing anoverwrap over a portion of the at least one outer layer.
 26. The methodof claim 25, including providing the overwrap by roll wrapping acomposite material over said portion.
 27. The method of claim 25,further including radially cutting the structural member along theportion containing the overwrap.
 28. A method of making a contouredstructural member, comprising providing at least one inner layercomprising a reinforced resin matrix material; providing at least oneouter layer over the at least one inner layer, the at least one outerlayer comprising a reinforced resin matrix material; providing anoverwrap over a portion of the at least one outer layer; connecting theat least one inner and outer layer to the at least one inner layer; andproviding an outer surface of the structural member with a polygonalshape.
 29. A method of making a contoured structural member, comprisingroll wrapping at least one inner layer comprising a reinforced resinmatrix material over a substrate; roll wrapping at least one outer layerover the at least one inner layer, the at least one outer layercomprising a reinforced resin matrix material; roll wrapping an overwrapover a portion of the at least one outer layer; connecting the at leastone inner and outer layer to the at least one inner layer; and providingan outer surface of the structural member with a polygonal shape.
 30. Acontoured structural member made by the method comprising: providing atleast one inner layer comprising a composite material; providing atleast one outer layer over the at least one inner layer, the at leastone outer layer comprising a composite material; connecting the at leastone inner and outer layer to the at least one inner layer; and providingan outer surface of the structural member with a polygonal shape.
 31. Acontoured structural member made by the method comprising: providing atleast one inner layer comprising a reinforced resin matrix material;providing at least one outer layer over the at least one inner layer,the at least one outer layer comprising a reinforced resin matrixmaterial; providing an overwrap over a portion of the at least one outerlayer; connecting the at least one inner and outer layer to the at leastone inner layer; and providing an outer surface of the structural memberwith a polygonal shape.
 32. A contoured structural member made by themethod comprising: roll wrapping at least one inner layer comprising areinforced resin matrix material over a substrate; roll wrapping atleast one outer layer over the at least one inner layer, the at leastone outer layer comprising a reinforced resin matrix material; rollwrapping an overwrap over a portion of the at least one outer layer;connecting the at least one inner and outer layer to the at least oneinner layer; and providing an outer surface of the structural memberwith a polygonal shape.